Electroconductive tape is used as an electromagnetic wave shield gasket that is attached, for example, to the casing of an electronic product in order to block electromagnetic waves. In the field of portable electronic devices such as cellular phones like smartphones, or electronic devices such as personal computers, making the devices more compact and improving performance is advancing. Together with having good adhesive properties and excellent grounding characteristics, electroconductive tape that is thinner is desired for use as the electromagnetic shield gasket of these electronic devices.
As disclosed in cited Patent Literature 1, for example, there are two kinds of conventional electroconductive tape: there is tape on which metallic foil or fabric such as non-woven fabric, having an adhesive layer in which electroconductive filler is dispersed as a base material, is layered on both sides; and there is tape that is composed only of an adhesive in which electroconductive filler is dispersed. When attempting to make the former electroconductive tape thinner, the adhesive layers must be made thinner. In doing so, the adhesive layers move into the uneven areas of the base material, and the tape loses its adhesive property. In order to improve the adhesive property, it is necessary to reduce the amount of electroconductive filler. As a result, the electroconductive characteristic decreases. In the latter electroconductive tape, it is easy to make the tape thinner because a base material is not used; however, the electroconductive characteristic is insufficient with filler alone, and there is a problem in that the tape is easily damaged when handled.
Moreover, the grounding characteristic is greatly influenced by the exposed state of the electroconductive filler that is included in the adhesive layer, and the state of contact with the base material. Therefore, there is also a problem in that a stable grounding characteristic cannot be obtained depending on the application condition. Furthermore, when the electroconductive tape includes a base material, making the base material itself thinner must be considered. However, when a non-woven fabric is made thin, the tensile strength greatly decreases, and so that there is a problem in that the electroconductive tape becomes torn or damaged during handling when applying the tape. When a metallic foil is used as the base material, there is a problem in that the adhesive layers may peel off due to deformation of the metallic foil.
Therefore, in order to solve these problems, cited Patent Literature 2 discloses an adhesive sheet having an adhesive layer formed on at least one side of a base material having an electroconductive property, with part of the base material protruding from the adhesive layer. Moreover, cited Patent Literature 3 discloses an electromagnetic wave shield tape that is a woven or knitted fabric that uses metal, or an electroconductive sheet that is formed into a net shape that is embedded into an elastomer base material, and that electroconductive sheet is exposed on both the front and rear sides of the elastomer base material.